1. FIELD OF THE INVENTION
The present invention relates to a pump system in a liquid supply system and, more particularly, to a piezo activated pump system in an ink liquid supply system for an ink jet system printer of the charge amplitude controlling type.
2. DESCRIPTION OF THE PRIOR ART
An ink jet system printer of the charge amplitude controlling type requires a small amount, constant flow rate pump system in order to ensure stable printing operation even when the ambient condition varies.
The conventional ink liquid supply system in an ink jet system printer of the charge amplitude controlling type employs a mechanical plunger pump of the constant flow rate type. However, the mechanical plunger pump does not ensure stable constant flow rate supply when the supply amount is very little. Furthermore, the mechanical plunger pump occupies a considerably large size.
To ensure stable constant flow rate supply even when the supply amount is very little, a piezo activated pump system has been proposed, wherein an piezo element is employed to vary the size of a pump chamber. An example of the piezo activated pump system is described in copending U.S. Patent Application, "INK LIQUID SUPPLY SYSTEM IN AN INK JET SYSTEM PRINTER OF THE CHARGE AMPLITUDE CONTROLLING TYPE", Ser. No. 510,355, filed on July 1, 1983 by Masaaki KURANISHI, Masahiko AIBA, Hideyuki MIYAKE and Naohiro OKU, and assigned to the same assignee as the present application. The Japanese counterpart is Japanese Patent Application No. 57-118240 filed on July 6, 1982; the British counterpart was filed on July 1, 1983 and assigned application No. 8317915; the German counterpart was filed on July 6, 1983 as P 33 24 397.2; and the Canadian counterpart was filed on July 5, 1983 and assigned Ser. No. 431,844.
In the piezo activated pump system describe in the abovementioned copending application, the pressure chamber is defined by a cylinder shaped piezo element. Therefore, the pressure chamber configuration is fixed to the cylinder shape. The cylinder configuration precludes effective removal of air bubbles from the pressure chamber when the air bubbles are included in the ink liquid supplied to the piezo activated pump system.
Furthermore, the pressure chamber surrounded by the piezo element mey explode when the ink liquid contained in the pressure chamber freezes. This is because the thin piezo element can not endure the expansion of the ink liquid when the ink liquid freezes. The freezing of the ink liquid will take place when the ink jet system printer is placed in a non-operating condition or when the ink jet system printer is transported from one office to another one in a low temperature atmosphere.